For various reasons, I have Thunderbird configured to default to compose plain text e-mails instead of HTML e-mails.

When I press <RETURN> to move to a new line, Thunderbird "helpfully" automatically inserts a second newline preventing me from formatting text like putting my name and address unless I compose it in something else like Word or Notepad and use copy/paste.A macro I have set up for the aforementioned name and address using the extension "quicktext" works fine.

How do I turn off that "helpful" extra blank space so that I can write something like

Thank you. I wonder how it got checked in the first place, as it just suddenly started happening when I haven't messed with the options in at least six months, not since they got rid of the company e-mail and made us use our own last spring.I assumed it was the latest updated that "helpfully" activated it.